1. Field
Example embodiments of the inventive concepts relate to high sensitivity image sensors, and more particularly, to high sensitivity image sensors that may be capable of sensing a single electron.
2. Description of the Related Art
An image sensor may transform photonic images into electric signals. Recent advances in computer and communication industries have led to strong demand for high performance image sensors in various consumer electronic devices including, for example, digital cameras, camcorders, PCS (Personal Communication System), game devices, security cameras, and medical micro cameras.
Widely-used CCD image sensors or CMOS image sensors may include a group of unit pixels which make up a unit picture element. Typically, a pixel may be made to a size of about 2 um. Although pixel size can be further reduced, it may be difficult to improve the performance of an image sensor when the size becomes less than about 1 um. This may be because of very narrow dynamic range, smaller full well capacity, and/or a Signal to Noise Ratio (SNR) drop to about 10-20:1. Further, conversion gain (efficiency of charge to voltage conversion) may be related to the capacitance of a photo detecting area. The more capacitance a photo detection area has, the less conversion gain it may have. When a device becomes small, relative capacitance may be increased and as a result the conversion gain may be decreased.
Accordingly, to reduce pixel size, it may be required to process signals with different structures and concepts from conventional image sensors.